The immunotherapy, called pembrolizumab (Keytruda), was most effective for patients whose tumours carry high levels of a molecule called PD-L1, according to the unpublished clinical trial results that will be presented at the 2019 American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago in the US.

But this was only seen when the immunotherapy drug was used alone. When combined with chemotherapy, it added no extra survival benefits to patients.

Dr. Hugo Ford, a Cancer Research UK-funded stomach cancer expert, said the results were “interesting,” but added that more data was needed on the potential survival benefits of immunotherapy for some patients.

Dr. Josep Tabernero, who led the study from the Vall d”Hebron Barcelona University Hospital and Institute of Oncology in Spain, said there remains a “significant unmet need for treatments for these cancers.” He believes that offering pembrolizumab as a first line treatment could provide “a new opportunity” for people newly diagnosed with cancers of the stomach or food pipe.

Finding the best responses

Immunotherapy drugs like pembrolizumab work by boosting patients’ immune systems to recognise and attack cancer cells.

The clinical trial included people living with advanced cancer located in the stomach or at the border between the stomach and the food pipe (oesophagus), also known as gastro-oesophageal junction cancer.

Of the 763 patients on the trial, 7 in 10 had stomach cancer and 3 in 10 had cancer at the border of the oesophagus and stomach—in all cases, the tumours didn’t carry a molecule called HER2.

Patients were randomly split into 3 groups and were given either:

chemotherapy

pembrolizumab

chemotherapy and pembrolizumab combined

Results show pembrolizumab was as effective as chemotherapy in prolonging survival in patients with advanced cancer. And for those whose cancer cells carry high levels of an important molecule called PD-L1, 4 in 10 patients (39%) taking pembrolizumab were alive 2 years after treatment, compared to just 2 in 10 (22%) of those treated with chemotherapy.

But the study found that combining the two treatments—a more expensive option—was no better than just treating patients with chemo.

Further evaluation needed

Ford said the results suggest that adding pembrolizumab to chemotherapy provides little benefit, while adding significant extra cost, even in tumours with high levels of PD-L1.

“But giving pembrolizumab alone to patients with tumours that have high levels of PD-L1 does look interesting, greatly improving survival. Further evaluation will be needed to strengthen and confirm this data,” he added.

Serious side effects were also less common among patients treated with pembrolizumab alone. 17 in 100 people taking pembrolizumab experienced severe side effects, compared with 69 in 100 of those taking chemotherapy.

But Ford cautioned about an overall message of immunotherapy being kinder to patients. “We need to be careful about saying that the toxicity of pembrolizumab is less than chemotherapy, because while that may be true for most, some patients treated with immunotherapy get very severe and enduring side effects,” he said.

Where did these results come from?

The ASCO annual meeting is the largest gathering of clinical cancer experts in the world.

Researchers share preliminary and more advanced results. These come from small, early stage studies through to large randomized clinical trials.